Flow Features in Shoulder Zone During Scroll Tool Friction Stir Welding Thick 6061 Aluminum Plates

The objective of this present study was to reveal the material flow interaction between the shoulder zone and nugget zone in a thick 6061 aluminum plate during scroll tool friction stir welding. It was observed via microstructural examinations that the scroll tool induces the bulk plasticized material to flow into the advancing side from the retreating side in the shoulder flow zone. This results in a unique flow pattern in the shoulder zone, including, among others, a near-half-onion ring pattern in the transverse section of the weld center. Moreover, a semi-circular pattern accumulated in the longitudinal direction of the bottom portion of the weld zone, but featureless in the top portion of the same weld zone. The obtained flow patterns have also been quantified in relation to the welding parameters to build a database for further and more detailed numerical investigation.